In 2008, 9.3% of children in the US had asthma. Due to the healthcare utilization and often lifetime duration of asthma, it is considered to be one of the costliest of chronic diseases (1), and disproportionally affects minorities and the poor (2). Ambient and traffic related air pollution increases the morbidity of childhood asthma, with greater risk among the socioeconomically disadvantaged (3). The objective of this project is to determine whether psychosocial stressors self-reported by a child modify the relationship between air pollution and childhood asthmatic symptoms and lung function in a population based cohort in Los Angeles, CA. This project will for the first time use data from the Los Angeles Family and Neighborhood Survey (L.A.FANS1-2), which collected self-reported psychosocial stressors from both the children and their primary caregivers. Importantly, this diverse sample has a large proportion of Hispanics (55%), and oversampled poor households. Researchers have hypothesized that psychosocial stressors, which tend to be higher in those with lower socioeconomic status, may explain some of the differential vulnerability to air pollution observed by socioeconomic status (4-8). Previous studies of stress and childhood asthma have primarily relied upon parents reporting their own stress levels (7-10), parent-reported neighborhood cohesion measures (6,11), or the child's exposure to violent acts (5). These measures, however, may misrepresent the psychosocial stress that a child perceives, as the relationship between the parent and child, the age of the child, the peer network of the child, and the child's own coping mechanisms may protect the child from the parent's own perceived stress. Using the child's self-reported psychosocial stressors to construct a holistic measure of their perceived stress from L.A.FANS data, the aims of the project are twofold; to determine whether a child's perceived stress level modifies the effect of air pollution on (1) asthmatic symptoms in children ages 9-17 and (2) lung function in children ages 5-17. The sub-aim is to determine if poor parent-child bonding in young children (ages 0-8) modifies the effect of air pollution on asthmatic symptoms. The project will utilize spatially highly refined land use regression models (LUR) for traffic related air pollutants (NO, NO2, NOX) that we constructed for the sample. This study will add to the previous literature by constructing a more holistic measure of the stress perceived by the child, and use that measure to determine if a child's perceived stress modifies their risk of asthma or reduced lung function from air pollution. By identifying risk factors that may contribute to childhood asthma, particularly in vulnerable populations such as those with low SES, we strive to reduce the enormous toll that childhood asthma has on children and their families.